This invention relates to automatic defrost timing circuits for refrigeration equipment such as refrigerators. In such equipment, a compressor controlled by a thermostat responsive to the temperature in a refrigerated enclosure pumps a refrigerant into condenser coils where the refrigerant is condensed giving off heat, and then the condensed refrigerant is expanded in evaporator or cooling coils absorbing heat and lowering the temperature within the refrigerated space; a defrost heater associated with the cooling coils is automatically cycled with the operation of the equipment by a defrost timer to melt ice formed on the cooling coils from humidity in the air within the refrigerated space.